This invention relates to a pressure lock controller and particularly to such a controller for a vacuum operated flow system.
In various flow systems, the pressure differential for establishing flow may include a downstream vacuum source. A temporary storage means such as a storage tank, a standpipe or the like within which liquid is stored until it reaches a selected level may be incorporated into the system. When such a selected level is reached, a discharge apparatus is actuated to remove liquid generally until a lower limit is established.
In vacuum operated sewage collection systems, for example, a standpipe is provided upstream of a main discharge valve. A vacuum collector is connected to and establishes a vacuum in the flow line for the transportation of the sewage. A particularly satisfactory two-position liquid level controller is disclosed in U.S. Pat. No. 3,777,778. The fluid sensor is mounted upstream of the discharge control valve and is connected to actuate a triggered controller having a fluid relay connected to charge a fluid timing capacitor which, in turn, actuates a fluid switch. The timing capacitor is preferably a storage device connected to atmospheric pressure through an adjustable resistor. When the output signal from the sensor if received, the vacuum connection to the capacitor is momentarily made and the vacuum established as a reference. The storage device signals the fluid switch which actuates a pilot valve to open the main valve. The sewerage flow continues until such time as the main capacitor has totally discharged, at which time the switch converts to an "off" condition, resetting the pilot valve and moving the main valve to a closed condition. The timing provides a constant volume of the liquid discharged per cycle independent of the input flow into the system. This is particularly significant in flow systems which rely on a slug or incremental liquid transfer in response to a given condition; such as a vacuum powered sewage transport system and the like.
The timer is a pressure triggered timer and is connected to the flow system as a pressure source. The timer is operable in response to an initial trigger or pulse signal from the sensor and accurately maintains a timing period over a considerable change in the supply or input pressure.
In operation of such vacuum operated systems, a low vacuum condition may be created in the sewer line between the main control valve and the vacuum source by low points in the flow line being filled by sewage and/or by a partial system bogdown or water logging. The sewage or water laying in the low points thus prevents creation of system vacuum and interferes with proper system operation. The system vacuum can be restored by admitting air into the system to force the sewage in such low points forward toward the collection station and clearing of such low points.